The present invention relates to an electric contact probe unit including an electroconductive needle member which is resiliently urged by a compression coil spring, and in particular to such an electric contact probe unit which is suitable for testing printed circuit boards, semiconductor devices and semiconductor wafers.
According to a conventionally known electroconductive contact probe unit for use in a contact probe for electrically testing electroconductive patterns of printed circuit boards and semiconductor products, each electroconductive needle member is received in a tubular holder so as to be axially slidable in and out of the holder and is resiliently urged by a compression coil spring in the direction to project out of the holder to the extent permitted by means for preventing the electroconductive needle member from completely projecting out of the holder. In such an electroconductive contact probe unit, a forward end of the electroconductive needle member is resiliently engaged by an object to be tested so that an electric signal may be transmitted between the object to be tested and an external circuit.
The applicant of this application previously proposed a contact probe unit arrangement in which a plurality of holes are passed through a plate-shaped support member as holders, and an electroconductive needle member and a compression coil spring are received in each of the holders so that a plurality of points of base boards and/or semiconductor devices may be measured or tested at the same time (Japanese patent laid-open publication No. 6-201725).
According to such an arrangement, as there is no need to prepare a tubular holder for each of the electroconductive needle members, and there is no need to prepare the holders as separate components, the spacing between adjacent electroconductive needle members can be minimized, and the contact probe can be adapted to highly densely arranged points to be tested.
To receive each electroconductive needle member and an associated compression coil spring, the plate-shaped support member is made from an electrically insulating synthetic resin plate or ceramic material. However, when the contact probe is provided with a support plate having a large area exceeding 100 mm in diameter, and is used in a high temperature environment, the relative positions of the holes (electroconductive needle members) could significantly change.
In view of such problems of the prior art, a primary object of the present invention is to provide a contact probe unit which is adapted to be highly densely arranged and to function properly even in a high temperature environment.
A second object of the present invention is to provide a contact probe unit of a highly compact design which is economical to manufacture, and yet capable of functioning properly even in a high temperature environment.
A third object of the present invention is to provide a contact probe unit of a highly compact design which is suited for mass production, and yet capable of functioning properly even in a high temperature environment.
The present invention achieves such objects by providing an electric contact probe unit, comprising; a holder formed by a holder hole passed through a holder member including at least a single plate member, the holder hole defining a small diameter portion on a first side of the holder member; a base board placed over a second side of the holder member, the base board including a circuit pattern aligned with an end of the holder hole on the second side of the holder member; an electroconductive needle member axially slidably received in the holder hole, and including a head portion adapted to project outwardly from the small diameter portion, and an annular shoulder adapted to be engaged by a corresponding annular shoulder defined at a base end of the head portion; and a compression coil spring received in the holder hole in a coaxial relationship to the electroconductive needle member to urge the head portion out of the small diameter portion; wherein the holder member consists of material having a low coefficient of thermal expansion.
Thus, owing to the low coefficient of thermal expansion, the positional errors of the locations of the contact probe units can be minimized even in a high temperature environment. By making the holder member from a plurality of laminated thin plate members, the work of forming the holes serving as holders is simplified, and is made suitable for mass production. In this case, the small diameter portion can be conveniently formed by reducing the size of the holder hole for the outermost one of the thin plate members jointly forming the holder member.
Materials having low coefficients of thermal expansion as well as other required mechanical properties can be readily found in silicon and metallic materials. However, metallic materials are generally electroconductive, and there is a need to insulate in the holder member from the electroconductive needle member. In view of difficulty in physically forming an insulating layer as the size of each contact probe unit is reduced, it is preferable if electrically insulating film is formed by a chemical reaction of the material of the holder member. Normally, such insulating film can be formed by oxidizing the material of the holder member, or by chemical vapor deposition, among other possibilities. When the holder member is made of silicon wafer, insulating film can also be formed by chemical deposition, and the insulating film preferably consists of silicon dioxide which is highly durable and chemically stable.
Preferably, the compression coil spring consists of electroconductive material, and is adapted to conduct an electric signal from the electroconductive needle member to the circuit pattern of the base board so that any additional means for conducting electric signal from the electroconductive needle member to the base board may not be required.